Adaptation by the Brown Planthopper to Resistant Rice: A Test of Female-Derived Virulence and the Role of Yeast-like Symbionts

Comparative Transcriptome Analysis Highlights the Role of NlABCG14 in the Honeydew Production of Virulent Brown Planthoppers (Nilaparvata lugens Stål) to Resistant Rice Variety

Brown planthoppers (BPHs, Nilaparvata lugens Stål) are a major threat to rice cultivation in Asia, necessitating the development of pest-resistant varieties for effective management. However, the adaptability of BPHs has resulted in the development of virulent populations, such as biotype Y BPHs, which exhibit significant virulence against the rice variety YHY15 that harbors the resistance gene Bph15. The various response mechanisms of BPH populations to resistant rice varieties are critical yet underexplored. Via RNA sequencing, the present study identified distinct transcriptional profiles in avirulent (biotype 1) and virulent (biotype Y) BPH nymphs both before and after feeding on YHY15 rice. Our findings revealed differential expression patterns of gene clusters involved in protein synthesis, hydrolysis, fatty acid biosynthesis, metabolism, cuticle composition, and translocation. Further analysis elucidated changes in the expression of genes associated with longevity and structural components of cuticles, highlighting specific disruptions in both biotype 1 and biotype Y BPHs. Moreover, the two biotypes showed differences in the expression level of genes involved in ATP-binding cassette (ABC) transporters. A functional assessment of ABC transporter genes revealed a role of NlABCG14 in the honeydew production of biotype Y BPHs to YHY15 rice, without impacting their survival and developmental dynamics. These insights deepen our understanding of the mechanisms of virulent BPHs response to resistant rice varieties and highlight potential targets for improving pest management strategies.

Virulence Adaptation by Rice Planthoppers and Leafhoppers to Resistance Genes and Loci: A Review

In recent decades, research on developing and deploying resistant rice has accelerated due to the availability of modern molecular tools and, in particular, advances in marker-assisted selection. However, progress in understanding virulence adaptation has been relatively slow. This review tracks patterns in virulence adaptation to resistance genes (particularly Bph1, bph2, Bph3, and bph4) and examines the nature of virulence based on selection experiments, responses by virulent populations to differential rice varieties (i.e., varieties with different resistance genes), and breeding experiments that interpret the genetic mechanisms underlying adaptation. The review proposes that varietal resistance is best regarded as a combination of minor and major resistance traits against which planthoppers develop partial or complete virulence through heritable improvements that are reversable or through evolutionary adaptation, respectively. Agronomic practices, deployment patterns, and herbivore population pressures determine the rates of adaptation, and there is growing evidence that pesticide detoxification mechanisms can accelerate virulence adaptation. Research to delay adaptation has mainly focused on gene pyramiding (i.e., including ≥ two major genes in a variety) and multilines (i.e., including ≥ two resistant varieties in a field or landscape); however, these strategies have not been adequately tested and, if not managed properly, could inadvertently accelerate adaptation compared to sequential deployment. Several research gaps remain and considerable improvements in research methods are required to better understand and manage virulence adaptation.

Gut yeast diversity of Helicoverpa armigera (Lepidoptera: Noctuidae) under different dietary conditions

Yeast is one of the important symbiotic flora in the insect gut. However, little is known about the gut yeast in Helicoverpa armigera (Lepidoptera: Noctuidae) under various dietary conditions. The composition and function of the intestinal yeast community also remain unclear. In this research, we explored the composition of yeast microorganisms in H. armigera larvae under different feeding environments, including apple, pear, tomato, artificial diet (laboratory feeding), Urtica fissa, Helianthus annuus, and Zinnia elegans (wild environment) using high-throughput sequencing. Results showed that a total of 43 yeast OTU readings were obtained, comprising 33 yeast genera and 42 yeast species. The yeast genera with a total content of more than 5% were Hanseniaspora (36.27%), Moesziomyces (21.47%), Trichosporon (16.20%), Wickerhamomyces (12.96%) and Pichia (6.38%). Hanseniaspora was predominant when fed indoors with fruits, whereas Moesziomyces was only detected in the wild group (Urtica fissa, Helianthus annuus, Zinnia elegans) and the artificial diet group. After transferring the larvae from artificial diet to apple, pear and tomato, the composition of intestinal yeast community changed, mainly reflected in the increased relative abundance of Hanseniaspora and the decreased abundance of Trichosporon. Simultaneously, the results of α diversity index indicated that the intestinal yeast microbial diversity of H. armigera fed on wild plants was higher than that of indoor artificial feeding. PCoA and PERMANOVA analysis concluded that there were significant differences in the gut yeast composition of H. armigera larvae on different diets. Our results confirmed that gut yeast communities of H. armigera can be influenced by host diets and may play an important role in host adaptation.

Timing of Fungal Insecticide Application to Avoid Solar Ultraviolet Irradiation Enhances Field Control of Rice Planthoppers

Thechemical control of rice planthoppers (RPH)is prohibited in annual rice-shrimp rotation paddy fields. Here, the fungal insecticides Beauveria bassiana ZJU435 and Metarizhium anisoplae CQ421 were tested for control of RPH populations dominated by Nilaparvata lugens in three field trials. During four-week field trials initiated from the harsh weather of high temperatures and strong sunlight, the rice crop at the stages from tillering to flowering was effectively protected by fungal sprays applied at 14-day intervals. The sprays of either fungal insecticide after 5:00 p.m. (solar UV avoidance) suppressed the RPH population better than those before 10 a.m. The ZJU435 and CQ421 sprays for UV avoidance versus UV exposure resulted in mean control efficacies of 60% and 56% versus 41% and 45% on day 7, 77% and 78% versus 63% and 67% on day 14, 84% and 82% versus 80% and 79% on day 21, and 84% and 81% versus 79% and 75 on day 28, respectively. These results indicate that fungal insecticides can control RPH in the rice-shrimp rotation fields and offer a novel insight into the significance of solar-UV-avoiding fungal application for improved pest control during sunny summers.

Slowing virulence adaptation in Asian rice planthoppers through migration-based deployment of resistance genes

Advances in molecular biology have accelerated rice breeding for resistance to Asian planthoppers. However, experience shows that planthoppers quickly adapt to resistance in tropical overwintering areas. With only limited sources available, the large-scale deployment of resistance genes can rapidly reduce the utility of these public goods. Planthoppers that migrate from tropical to temperate Asia carry virulence against many resistance genes, but adapt more slowly to resistant rice in temperate regions. Therefore, by restricting deployment of selected genes to temperate regions, virulence-adaptation rates and the volume of migrants returning to overwintering sites could be reduced. The current open exchange of breeding materials throughout Asia urgently requires an international, multidisciplinary, stakeholder coalition to promote a more sustainable deployment of planthopper-resistant rice.

Fitness costs of resistance to insecticide pymetrozine combined with antimicrobial zhongshengmycin in Nilaparvata lugens (Stål)

The brown planthopper, Nilaparvata lugens (Stål), is a major pest of rice crops, and its control is critical for food security. Pymetrozine has been recommended as an alternative to imidacloprid for controlling N. lugens, but the pest has developed high resistance to it, making its prohibition and restriction urgent. To address this issue, we conducted a study using a mixture of pymetrozine and zhongshengmycin with the effective ratio of 1:40, to evaluate the fitness costs in N. lugens. Our results showed that N. lugens had a relative fitness of 0.03 under this ratio, with significantly reduced longevity, female and male adult periods, total pre-oviposition days, and fecundity. Moreover, the expression levels of the uricase gene (EC1.7.3.3) and farnesyl diphosphate farnesyl transferase gene (EC2.5.1.21) were reduced in N. lugens. These genes are involved in urea metabolism and steroid biosynthesis pathway, respectively, and their suppression can interfere with the normal nutritional function of N. lugens. Our study demonstrates that the combination of chemical insecticides and antimicrobials can delay the development of resistance and improve the efficiency of pest control. This information is valuable for researchers developing management strategies to delay the development of pymetrozine resistance in N. lugens.